1. Field Of The Invention
This invention relates to new types of ring-opened, addition organic polymers such as polyoxyethylenepolyoxypropylene polymers and methods for making them. In particular, the present invention is concerned with novel ring-opened, addition type polymers with controlled monomer sequence distributions and processes for making them.
2. Prior Art
A wide variety of polymers made from one or more cyclic, organic monomers capable of ring-opening, addition polymerization are in extensive use for a wide range of applications. For example, copolymers of ethylene oxide and propylene oxide represent a particularly fruitful area in which to apply the present invention as a tool for tailoring performance characteristics. This is so because these two monomers form respective homopolymers which, although generally similar in glass transition temperatures, are basically dissimilar in solubility characteristics. Poly(ethylene oxide) for example, is a water soluble polymer which hydrogen bonds extensively in aqueous solution. Poly(propylene oxide), on the other hand, is an oil soluble polymer with greatly reduced tendencies toward hydrogen bond formation. When these two monomers are copolymerized, therefore, the products which result exhibit both hydrophilic and hydrophobic character to an extent dependent upon both the overall composition and the structure of the copolymer in terms of monomer sequence distribution.
Block copolymers of ethylene oxide and propylene oxide have very distinct surface active characteristics. They are efficient surface tension reducers in aqueous solutions and function as surfactants, wetting agents, and emulsifiers. The block copolymer structure thus maximizes the performance characteristics of such copolymers in all areas which depend upon well-defined hydrophile and hydrophobe structure. There is currently marketed a broad line of such oxide copolymers, their product line being presented in the form of a grid whose axes are molecular weight of the hydrophobe block (propylene oxide block) and overall hydrophile content (weight percent ethylene oxide). As a further consequence of the block structure, these commercial copolymers have the ability to gel water solutions at certain rather high fluid concentrations. This property is utilized in the preparation of a broad line of clear ringing gels for applications such as antiseptics, cosmetics, sun-screening agents, hair bleaches and the like. Because of their structural homogeneity within the hydrophile and hydrophobe segments, block copolymers are often pastes or solids at ambient temperatures.
Conventional random copolymers of ethylene oxide and propylene oxide lack the pronounced surface active characteristics of their blocked counterparts. Thus, they have been much poorer reducers of surface tension in aqueous solutions and are generally poorer wetting agents, surfactants and emulsifiers. This behavior is a direct consequence of the random structure, which does not permit the formation of lengthy chains of either hydrophile or hydrophobe portions. Because of their structural heterogeneity, random copolymers are generally liquids at the same molecular weights and overall compositions where their blocked counterparts are solids or pastes. A considerable number of random ethylene oxide-propylene oxide copolymers are commercially available but, unlike the block copolymers, the random structures do not gel water. They find applications which stress their utility as functional fluids such as pump lubricants, quenching fluids in foundary operations, brake fluids, "pusher" fluids in drilling operations and the like. Inasmuch as these random structure fluids form homogeneous aqueous solutions, they can be used advantageously as base components for non-flammable functional fluids.
Heretofore, the only types of oxide copolymers known to the art have been the block and random types which, as we have seen, are characterized by widely divergent properties. The present invention is ideally suited to the preparation of an infinite number of different structural species intermediate between the block and random extremes. In accomplishing these structural alterations by this invention, it is observed that certain solution properties of these copolymers change accordingly. The present invention therefore represents a simple and convenient means for tailoring the structure of such copolymers so as to generate various desired solution properties of a type intermediate between those exhibited by random and block copolymers. Exemplary of the solution properties which can be altered by this technique are aqueous and non-aqueous solution viscosity, wetting ability, foam stability, cloud point, and surface tension. Additionally, the present invention makes possible the preparation of liquid fluids with properties very similar to the one of block copolymers which are solids or pastes.
Another aspect of this invention relates to the control of the occurrence of primary and secondary hydroxyls in the terminal groups of the copolymers. Generally, the ring-opening addition copolymerization is initiated by any of the well known active hydrogen containing initiators which include alcohols, amines, thiols, carboxylic acids or the corresponding di- or trifunctional initiators and the polymerization can be acid-catalyzed or base-catalyzed. The ring-opened addition copolymer thus produced has one or more terminal hydroxyl groups in accordance with the functionality of the initiator. Since the terminal hydroxyl groups are highly reactive, these copolymers are useful as intermediates in the production of many commercially important classes of compounds including polyesters, polyurethanes, polyacetals, polysiloxanes, polyethers and polycarbonates.
Each terminal hydroxyl group of the ring-opened addition copolymer can be a primary or secondary hydroxyl group, depending on the nature of the mer unit to which the terminal hydroxyl group is bonded. Those skilled in the art will recognize that during the polymerization certain cyclic organic monomers, such as ethylene oxide and tetrahydrofuran, undergo ring-opening addition to the polymer chain in such a way as to form primary hydroxyl terminal groups in most instances (hereafter referred to as "primary hydroxyl forming monomers"), while other cyclic organic monomers undergo ring-opening addition to the polymer chain in such a way as to form secondary hydroxyl terminal groups in most instances (hereafter referred to as "secondary hydroxyl forming monomers"). Thus, for example, a copolymer of ethylene oxide (a primary hydroxyl forming monomer) and propylene oxide (a secondary hydroxyl forming monomer) has primary hydroxyl terminal groups at most of the sites at which the last mer unit added to the polymer chain is an ethylene oxide derived mer unit and secondary hydroxyl terminal groups at most of the sites at which the last mer unit added to the polymer chain is a propylene oxide derived mer unit.
In copolymerizing one or more cyclic organic monomers of the primary hydroxyl forming type (e.g., ethylene oxide) and one or more cyclic organic monomers of the secondary hydroxyl forming type (e.g., propylene oxide) it is highly desirable to be able to control the ratio of primary to secondary hydroxyl terminal groups in the resultant copolymer. Since primary hydroxyl groups are more highly reactive than secondary hydroxyl groups, this ratio affects the rate of reaction of the copolymer with other reactive compounds. While it is frequently desired to maximize the rate of reaction of the copolymer with other reactive compounds for economic reasons, one may also desire to react the copolymer with another compound at a relatively slow controlled rate of reaction. For example, in reacting the ring-opened addition copolymer with an isocyanato compound to produce a polyurethane resin, one may desire a slow reaction rate to increase the pot life of the resin. Moreover, the ratio of primary to secondary hydroxyl terminal groups affects the distribution of reaction products in certain reactions of the copolymer such as, for example the distribution of ketones and aldehydes which are obtained upon oxidation of the terminal hydroxyl groups of the copolymer.
In the prior art, copolymers produced by the ring-opening addition copolymerization of one or more cyclic organic monomers of the primary hydroxyl forming type and one or more cyclic organic monomers of the secondary hydroxyl forming type (hereafter called "mixed hydroxyl end group copolymers") have offered little control over the ratio of primary to secondary hydroxyl terminal groups. Mixed hydroxyl end group copolymers produced by conventional block copolymerization are terminated predominantly by primary hydroxyl groups or predominantly by secondary hydroxyl groups, depending on whether the last monomer fed to the polymerization reactor is of the primary or secondary hydroxyl forming type. Mixed hydroxyl end group copolymers produced by conventional random copolymerization have a ratio of primary to secondary hydroxyl end groups which is substantially fixed for any given ratio of primary to secondary hydroxyl forming monomers in the feed stream. Thus, it can be seen that the ratio of primary to secondary hydroxyl terminal groups in mixed hydroxyl end group copolymers produced by these methods is dependent on the overall structure of the copolymer chain. This is undesirable since it may preclude the skilled worker in the art from producing a mixed hydroxyl end group copolymer having both the optimum ratio of primary to secondary hydroxyl terminal groups and the optimum overall copolymer chain structure for a particular end use. As was previously discussed, the overall monomer sequence distribution in the polymer chain affects important properties such as solution properties, state of aggregation (i.e. solid or liquid) etc.
Heretofore, there have not been available mixed hydroxyl end group copolymers having ratios of primary to secondary hydroxyl terminal groups which can be varied independently of the overall copolymer chain structure.
Certain process techniques disclosed in U.S. Pat. No. 3,804,881, and to some extent disclosed in U.S. Pat. No. 3,839,293, may be employed in the practice of this invention. However, the polymers of this invention are not disclosed in either of these patents. The polymers disclosed and claimed herein are new and possess unexpected beneficial properties not heretofore attained for polymers made from the same monomers. Attention is also drawn to U.S. Pat. Nos. 3,427,287; 3,448,173 and 2,562,235 and British Pat. No. 1,292,226. None of these latter patents disclose the polymers of this invention or techniques for making them. No other more pertinent prior art is known.